Surface plate and controls therefor

ABSTRACT

A granite surface plate which is provided at its undersurface with a controlled source of heat. Temperature sensors are used as controls to apply and vary the heat in a manner to maintain the upper surface of the plate flat, irrespective of a changing temperature gradient to which the surface plate may be subjected.

United States Patent 1191 11 3,739,151? Rahn June 12, 1973 1 SURFACE PLATE AND CONTROLS 3,267,728 8/1966 Solomon 73/190 R THEREFOR 2,955,184 10/1960 Grindrod 219/448 3,549,864 12/1970 Borer 219/497 [75] Inventor: Rudolph J. Rahn, Dayton, Ohio [73] Assignee: Rahn Granite Surface Plate Com- P'imary EXami"e'Bemard Gilheany pany Dayton Ohio Assistant ExaminerF. E. Bell Att0rneyJer0me P. Bloom [22] Filed: Jan. 5, 1971 [21] Appl. No.: 104,004 [57] ABSTRACT A granite surface plate which is provided at its under- 52 (:1 217 443 33/174 H 219/497 surface with a controlled source of heat. Temperature [51] Int. Cl. 1105b 1/02 Sensors are used as controls to pp y and y the heat [58] Field 61 Search .7 219/448, 449, 450, in a manner to maintain the pp Surface of the Plate 219/497 494; 73 155 190 R, 359; 33 174 H flat, irrespective ofa changing temperature gradient to which the surface plate may be subjected. [56] References Cited 9 Claims, 2 Drawing Figures 7 mrvewron RUDOLPH J. RAHN "2km 7? @Zmw A TTOR/VE Y SURFACE PLATE AND CONTROLS THEREFOR BACKGROUND OF THE INVENTION This invention realtes to surface plates and more particularly to a surface plate provided with improved means for control of its upper or reference surface.

A surface plate is a precision device. It is originally constructed with the objective to produce thereon an upper orworking surface which is uniformly flat or which conforms, in the first instance, to a substantially flat segment of a sphere. Apart from any difficulty in achieving the original plate, problems in the use thereof derive from the fact that the normal ambient temperature gradient in a place of use produces a temperature differential between its upper and lower surface. Under normal conditions, this will cause the top of the plate to be subjected to a slightly higher temperature than the bottom. The result is a slight bow in the plate and a correspondingly bowed upper or working surface. To illustrate, it has been found, experimentally, that a granite surface plate 8 long will bow convexly 0.0004 inches when subjected to a temperature gradient of 0. 1 F., per 1 inch of elevation, the coefficient of thermal expansion of granite being 3.5 millionth of an inch per 1 F. change in temperature. Under ordinary circumstances, therefore, a surface plate will soon assume a working configuration somewhat different from that originally intended. Even with air conditioning, this configuration may vary from season to season of the year and depending on the particular location of the plate. For that matter, the working surface of the plate is sensitive to any condition producing a temperature differential from one portion of the plate to the other. When heating a room, the warm air is usually introduced near the upper part of the room. The warmest air will be near the ceiling, with cooler air at lower heights. Under the influence of air conditioning, where cold air is introduced at the ceiling of a room in which the surface plate is used, there may even be, under some conditions, a situation where the plate is subjected to a small negative gradient. In this last case, the temperature at the upper surface of the plate will be slightly lower than the temperature at the lower surface, producing a resultant concavity in the working surface.

While efforts have been made in the prior art to reduce or to compensate for the effects of temperature gradient and changing temperature gradient, the results are not completely satisfactory. In the prior art the mechanisms employed to solve the problem have usually involved air flow arrangements which are complex in effect and are not readily controlled. There has been some success with certain solutions involving control of air flow about a surface plate but on the whole accurate control of the temperatures to which a surface plate is subjected has proven very difficult.

SUMMARY OF THE INVENTION The present invention affords a very simple solution to the above-mentioned problems. It provides for means to apply, as and when required, a controlled heat to the undersurface of a surface plate, which heat, in any event, is directed to achieve a condition in the upper or reference surface of the plate so as to maintain it essentially flat. For such purpose, the invention contemplates any controllable heat source, for example, a radiant heating means, being disposed under the surface plate. In connection with the radiant heating means is a control unit which receives signals from temperature sensors applied respectively adjacent the top surface of the plate and to its bottom. The control unit is conditioned to energize the heat source when the respective temperature sensors sense a departure from a predetermined and preset temperature relation between that existing at the upper surface of the plate and to its bottom. For a certain surface plate, once the control unit is set to recognize acceptable temperature signals from the sensors, any departure from such signals will cause it to respond to produce an increase or decrease in heat emanating from the heat source.

It is accordingly a primary object of the invention to provide a surface plate with suitable controls rendering it more efficient and satisfactory in use, adaptable to a wide variety of applications and unlikely to malfunction.

A further object of the invention is to provide simple means to obviate the effect of a changing temperature gradient upon a surface plate.

Another object of the invention is to provide means to control the temperature of the surface opposite the working surface of a surface plate by applying thereto an external heat source in a manner that one may maintain the working surface of the plate essentially flat.

A further object of the invention is to provide means for applying heat to a surface plate in a radient form so 'as to maintain a prescribed condition of its upper or working surface without the need of apparatus for con trolling the movement of air in the vicinity of the plate.

An additional object of the invention is to provide means enabling a surface plate having convexities in its working surface to be corrected substantially to its desired configuration without need for structural modification thereof.

A further object of the invention is to provide a surface plate with improved and simplified controls for maintaining a prescribed condition of its working surface which possess the inherent meritorious characteristics and the means and mode of use herein described.

With the above and other incidental objects in view as will more fully appear in the specification, the invention intended to be protected by Letters Patent consists of the features of construction, the parts and combinations thereof, and the mode of operation as hereinafter described or illustrated in the accompanying drawings, or their equivalents.

Referring to the accompanying'drawing wherein is shown one but obviously not necessarily the only form of embodiment of the invention,

FIG. 1 is a perspective view of a surface plate and in conjunction therewith a diagrammatic illustration of the controls therefor in accordance with the invention; and

FIG. 2 is a diagrammatic showing, in cross section, of the radiant heat source employed and its relation to the undersurface of the illustrated surface plate.

Referring to the drawings, apparatus as there illustrated is applied to a granite surface plate 10, which, as shown, is rectangular in form. In accordance with the preferred practice of the invention, the upper surface of the plate 10 is in the first instance appropriately fmished to provide it with a uniform flat convex shape. It should assume the shape of the outer surface of a segment of a sphere'of extremely large radius. As will be further described, the surface 11 when so shaped in the first instance, can be readily converted to a completely flat reference plane in a most simple fashion.

The bottom or underside 12 of the plate is shown to rest in an open rectangular frame 13 which is supported at its corners by legs 14. Thus, as illustrated, the surface plate is relatively elevated from a base surface S, and the frame 13, being open, exposes the undersurface of the plate to an open area. This, of course, means that due to natural conditions the undersurfaces of the plate will be exposed to a slightly different temperature than the upper surface thereof.

As diagrammatically shown in the drawings, in a highly simplified presentation, several sources 15 of radiant heat are disposed on the surface S in a symmetrical pattern of exposure within the periphery of the frame 13 and below the undersurface 12 of the plate 10. For simplicity of illustration, the sources of heat 15 are shown as electric light bulbs rectangularly arranged and mounted in individual fixtures 16, commonly wired by .conductors 17, in known manner, so they may be simultaneously energized to a degree and as and when required. As will be self-evident, when the bulbs 15 are energized they will radiate heat in a uniform pattern which is applied directly to the undersurface 12 of the plate 10. The arrangement of the heat sources will in any case be such to enable a substantial uniform heating of the undersurface of the plate 10, as and when required. Inserted in the circuit provided for energizing the bulbs 15 and suitably and commonly connected thereto by a conductor segment 17a is a control unit 18 from which extends a conductor at the remote extremity of which is a male plug which may be applied to a conventional electrical receptacle in the room where the surface plate is in use. This last conductor is identified by the numeral 19 and the connected plug by the numeral 21.

Attention is directed to the temperature sensors 24 and 25 shown in the drawings, the first of which is applied to a side of the plate 10, adjacent its upper surface. In the example illustrated the sensor 25 is applied to the undersurface of the plate 10, at its approximate center. Each sensor is releasably attached, for example as by being taped to the plate exterior. Accordingly,

two sensors are provided, respectively arranged to sense the temperature at the upper and lower surfaces of the plate 10. From the sensors 24 and 25 respectively extend conductors 22 and 23 the remote extremities of which are interrelated to a conventional control medium in the control unit 18.

The control unit 18 is not disclosed in detail since in and ofitself it is in a large part comprised of electronic components of known operating characteristics which are well known to a mechanic versed in the art. As shown, the operating components are enclosed in a housing 26 which may be constructed for attachment to one end of the surface plate. In the alternative it may, of course, be disposed in a detached adjacent relation to the plate. In any event, it provides therein suitable connections for the conductors 17a, 19, 22 and 23. In the front face of the housing is embodied a rotatable dial 27 having a centrally projected knob 28. The latter facilitates the rotation of the dial as and when required. [n the process of rotation, an arcuate series of graduations 29 formed on the dial are turned relatively to a fixed indicator 31 centered in adjacent relation to the dial on the face of the housing. As shown, the graduations 29 include a zero position and a series of minus and plus graduations respectively to either side thereof. lnteriorly of the housing are conventional means to continuously receive signals from the sensors 24 and 25 and to compare the differential, if any, between the signals. The conventional circuitry contemplates that in accordance with a prescribed setting of the dial 27 that as long as predetermined temperature signals are received from the sensors and compared, the flow of energy to the bulbs 15 is interrupted. Correspondingly, in the event the temperatures sensed by the sensors 24' and 25 should show a differential to thereby depart from the preset accepted temperatures sensed thereby, then the signal receiving means will close a switch to thereby close a circuit from the source of power to the bulbs, in which event the bulbs are energized and radiant heat caused to emanate therefrom. Depending on the location of the plate and the nature thereof, the unit can be tested to determine what temperature differential, if any, is required between the upper surface 11 and the undersurface 12 to create a flat reference plane in the surface 11 as required. Once this is achieved, this will determine the normal setting of the dial 27, which in turn controls the setting for the signal receiving means.

It will thus be seen that as long as the sensors signal the desired temperatures at and the temperature differential between the upper and lower surface of the plate, a comparison thereof within the control unit 18 by the signal receiving mechanism having in connection therewith the normally open control switch will prevent lighting the bulbs. When the sensors show an unacceptable differential, the mechanism in the control unit 18 will automatically respond to close the switch and complete a circuit from the source of power to the bulbs so that the bulbs light up and radiate heat upon the undersurface 12.

[n the great majority of the instances a departure from the prescribed temperatures will indicate a convexity in the working surface of the plate 10. As the heat is emanated and absorbed by the surface plate, there is eventually restored a desired temperature relation between the upper and lower surfaces of the plate which will indicate that there is achieved an essentially planar working surface thereon.

It will be seen, therefore, that in the practice of the invention one may maintain a temperature relation of the upper and lower surface of the plate which will insure that the operating surface thereof defines a plane irrespective of temperature gradient or changes thereof in the area in which the plate is used.

Considering further the dial 27, in general, where it is desired to produce a more concave effect in the upper surface of the plate 10, the dial control is turned in the minus direction. If a more convex configuration is desired the control is turned in the plus direction. The settings and effect thereof will definitelybe determined by the nature of the original plate as well as the conditions under which it is to be used.

As indicated herein, in the original contouring of the working surface of the plate 10, it should be made as nearly to the shape of a uniform convex surface corresponding to a relatively flat outer surface of a segment of a sphere of very large radius. This is desirable since radiant temperature affects the surface of the plate in a spherical manner by changing the radius of the sphere in such instance. According to the present invention, a setting of the dial 27 is possible that with a predetermined application of heat one can draw down the surface 11 to a flat planar configuration. This having been established, the temperature sensors will turn the heat on and off, automatically, as required, to keep the temperature differential at the upper and lower surface of the plate which dictates the best planar working surface at the required setting. I

Another use of the disclosed system makes it possible, for example, to shut off the heat source when the surface plate is to be subjected to heavy loads. This would allow the basic spherical surface under the settings established to reassume its convex configuration to offset the normal sag'which might occur due to the load.

Also, in the event the surface 11 should become worn and tend thereby to assume a concave configuration, by adjustment of the control unit, in a conventional manner, it would be possible to compensate for this condition and reduce the increments of heat applied to enable the necessary control of the working surface.

As will be self-evident, the system here illustrated may be applied to any existing surface plate installations which may have a convex surface with equal effectiveness. In some instances the placement of the sources of radiant heat may be varied to meet the required needs. Also, other sources of radiant heat may be utilized than that here illustrated, radiant heat being the preferred medium.

In any event, the invention provides that when a working surface of a surface plate departs from a prescribed mean there is automatically energized and deenergized a source of radiant heat which is applied to the undersurface of the plate. Heat will and can be turned on and off, automatically, as required for the prescribed temperatures at the upper and lower surface of the plate to achieve a flat, uniform, planar surface 11.

The control unit 18 may include also a variable resistor means of any conventional nature enabling a control of the voltage applied to the bulbs as and when required under the particular circumstances and conditions at hand. Such resistor may be embodied in the line from the source of power to the bulbs. For precision control, it will be seen that the voltage delivered may be represented by an adjustable dial (not shown) having calibrations referenced to calibrations on the housing for the control unit. Thus one can, simply by adjusting the dial, predetermine, as will be obvious, the nature and the degree of energizing of the bulbs 15 and thereby the degree of radiant heat that will result and be applied to the undersurface of the plate 10 in any one instance.

From the above description it will be apparent that there is thus provided a device of the character described possessing the particular features of advantage before enumerated as desirable, but which obviously is susceptible of modification in its form, proportions, detail construction and arrangement of parts without departing from the principle involved or sacrificing any of its advantages.

While in order to comply with the statute the invention has been described in language more or less specific as to structural features, it is to be understood that the invention is not limited to the specific features shown, but that the means and construction herein disclosed comprise but one of several modes of putting the invention into effect and the invention is therefore claimed in any of its forms or modifications within the legitimate and valid scope of the appended claims.

Having thus described my invention, I claim: 1. The combination comprising a surface plate sub- 5 ject to bowing in a room in which ambient temperatures reflect a vertical gradient, supplemental heat applying means arranged to heat a lower surface of the plate exclusively of an upper surface, and means utilizing said supplemental heat applying means to maintain a temperature at said lower surface which may substantially correspond to or be specifically different from the temperature at said upper surface to obviate temperature gradient effects or to cause the plate to bend into its most nearly flat contour said temperature maintaining means comprising individual means for sensing the temperature of said plate at its said upper and lower surfaces, and means responsive to selected differences in sensed temperatures for controlling said heat applying means.

2. Apparatus according to claim 1, wherein said last named means is selectively operable to increase or reduce temperature at said lower plate surface compensating for wear or use effects on said upper surface.

3. Apparatus according to claim 2, wherein said means -responsive to selected temperature differences comprises a control settable in one direction if a more concave upper plate surface is desired or in an opposite direction if a more convex upper plate surface is desired.

4. Apparatus according to claim 3, wherein said control is operative through said heat applying means to maintain a constant differential between upper and lower temperatures irrespective of variations in the ambient temperature gradient between said surfaces.

5. Apparatus according to claim 1, characterized by means mounting said surface plate in a relatively elevated position exposing said lower surface, said heat applying means comprising an energizable and deenergizable radiant heat source disposing beneath to uniformly heat said lower surface when energized.

6. Apparatus according to claim 5, wherein said radiant heat source is controlled by said temperature maintaining means, said temperature maintaining means comprising thermistors attached to the surface plate to sense temperatures at said upper and lower surfaces thereof, and further comprising means to energize and deenergize said radiant heat source at different high and low temperature differentials as sensed by said thermistors.

7. Apparatus according to claim 6, wherein said energizing and deenergizing means is adjustable to regulate the heat input into said lower plate surface to cause the plate to bend into its most nearly flat contour.

8. The combination comprising a surface plate which may have been made convex beyond tolerance, means to effect a continuous correction of such excess convexity in the use of the plate by heating a lower surface of the plate to a temperature value higher than an upper surface, said means including a heat source capable of being regulated and arranged with respect to the surface plate to apply heat to the said lower surface thereof exclusively of the upper surface said means further including sensors sensing the temperature of the surface plate substantially at upper and lower surfaces thereof, and a controller responding to sensed temperature differentials to regulate said heat source.

9. Apparatus according to claim 8, wherein said controller is adjustable to vary the input of heat into the lower plate surface in accordance with the extent of convexity to be corrected. 

1. The combination comprising a surface plate subject to bowing in a room in which ambient temperatures reflect a vertical gradient, supplemental heat applying means arranged to heat a lower surface of the plate exclusively of an upper surface, and means utilizing said supplemental heat applying means to maintain a temperature at said lower surface which may substantially correspond to or be specifically different from the temperature at said upper surface to obviate temperature gradient effects or to cause the plate to bend into its most nearly flat contour said temperature maintaining means comprising individual means for sensing the temperature of said plate at its said upper and lower surfaces, and means responsive to selected differences in sensed temperatures for controlling said heat applying means.
 2. Apparatus according to claim 1, wherein said last named means is selectively operable to increase or reduce temperature at said lower plate surface compensating for wear or use effects on said upper surface.
 3. Apparatus according to claim 2, wherein said means responsive to selected temperature differences comprises a control settable in one direction if a more concave upper plate surface is desired or in an opposite direction if a more convex upper plate surface is desired.
 4. Apparatus according to claim 3, wherein said control is operative through said heat applying means to maintain a constant differential between upper and lower temperatures irrespective of variations in the ambient temperature gradienT between said surfaces.
 5. Apparatus according to claim 1, characterized by means mounting said surface plate in a relatively elevated position exposing said lower surface, said heat applying means comprising an energizable and deenergizable radiant heat source disposing beneath to uniformly heat said lower surface when energized.
 6. Apparatus according to claim 5, wherein said radiant heat source is controlled by said temperature maintaining means, said temperature maintaining means comprising thermistors attached to the surface plate to sense temperatures at said upper and lower surfaces thereof, and further comprising means to energize and deenergize said radiant heat source at different high and low temperature differentials as sensed by said thermistors.
 7. Apparatus according to claim 6, wherein said energizing and deenergizing means is adjustable to regulate the heat input into said lower plate surface to cause the plate to bend into its most nearly flat contour.
 8. The combination comprising a surface plate which may have been made convex beyond tolerance, means to effect a continuous correction of such excess convexity in the use of the plate by heating a lower surface of the plate to a temperature value higher than an upper surface, said means including a heat source capable of being regulated and arranged with respect to the surface plate to apply heat to the said lower surface thereof exclusively of the upper surface said means further including sensors sensing the temperature of the surface plate substantially at upper and lower surfaces thereof, and a controller responding to sensed temperature differentials to regulate said heat source.
 9. Apparatus according to claim 8, wherein said controller is adjustable to vary the input of heat into the lower plate surface in accordance with the extent of convexity to be corrected. 